s390/pai_crypto: Rename paicrypt_root_alloc() and paicrypt_root_free()

s390/pai_crypto: Rename paicrypt_root_alloc() and paicrypt_root_free()

To support one common PAI PMU device driver which handles
both PMUs pai_crypto and pai_ext, use a common naming scheme
for structures and variables suitable for both device drivers.
Rename functions paicrypt_root_alloc() and paicrypt_root_free()
to pai_root_alloc() and pai_root_free().
No functional change.

Signed-off-by: Thomas Richter <tmricht@linux.ibm.com>
Reviewed-by: Jan Polensky <japo@linux.ibm.com>
Signed-off-by: Heiko Carstens <hca@linux.ibm.com>